Time of supply of service in other cases :
Where it is not possible to determine the time of supply of services in any of the above manner. The time of supply shall (a) in a case where a periodical return has to be filed, be the date on which such return is to be filed; or (b) in any other case, be the date on which the CGST/SGST is paid – section 13(5) of CGST Act.